Controllable kites may have one, two, three, four or more control strings, or control lines.
Single string kites of the genre known as Fighting Kites, made and used in India and the Far East for hundreds of years, made usually from tissue paper and split bamboo, are small cheap and expendable. They use the instability of a flat plane, and the stability given to that flat plane when pressure is applied through the bridle, string and airflow, to form a stable vee shape. Held at a constant angle by the bridle, the kite is driven forwards in the direction the kite is facing at the time pressure is applied. When pressure on the string is released, the kite once more returns to a flat plane, becomes directionally unstable, and turns until pressure is once more applied.
Kites controlled by two lines generally have a rigid frame, the aerodynamic form being determined by the way in which the sail is attached to the frame. They can only move in a forward direction, relative to the airflow over them, right and left turns being controlled by the lengthening and shortening of the control lines, generally attached to the kite's bridle.
Kites controlled by three and more control lines (multiple control-lines) can be made to fly in any direction: forwards, backwards, or sideways and can be made to hover and spin on their axis at the command of the control lines. Each line length, on a multiple control line kite, can be adjusted relative to another whilst the kite is in flight. The flyer can, thus, change the angle of the airflow over the whole, or part, of the kite. This allows total control over the kite's attitude, direction and speed.
All previously known multi-string kites, with the exception of those derived from a ram-inflated airfoil shape, have had a relatively rigid frame that predetermines the shape and the aerodynamic form, prior to flight. This rigid frame may be a complex shape, with the sail stretched tightly over it, conforming to that frame shape, or it may be a rigid frame with the kite sail attached loosely, the cut of the sail and the billow of the sail under the pressure of the wind producing a stable aerodynamic shape.
Ram-inflated airfoil designs, whilst non-rigid when uninflated, rely on positive air pressure during flight to produce a shape that is semi-rigid and unable to vary its geometry or intrinsic stability and flying characteristics. Moreover, because of the need for positive air pressure to remain inflated, these designs have limited manoeuvrability and reverse-flight capability.
Also, previously known multi-string kites have generally required a complex system of bridle rigging strings and, in some instances, complicated control handles to provide adequate flying characteristics. These bridling strings are often complex and generally require minute and frequent adjustment to maintain kite performance under differing conditions. This adjustment is generally difficult to achieve and time-consuming.
Current multi-string controllable kites are limited by the rigidity of their design. The designer must choose to produce either an aerodynamic form with low stability suitable for maximum manoeuvrability at low forward speeds or an aerodynamic form suitable for high speed use with high stability and good acceleration. Current designs must, therefore, compromise one or both ends of aerodynamic performance and so fail to provide the optimum performance for the kite flyer.
U.S. Pat. No. 4,892,272 discloses a kite with four control lines and a leading edge support member to which are freely attached wing struts, one at each side thereof. A bridling arrangement is employed to correct the control lines to the support member and the wing struts.